High pressure contacts



g- 1956 w. KOWALSKI EIAL 2,760,034

HIGH PRESSURE CONTACTS Filed Oct. 28, 1953 I 2 Sheets-Sheet l MLTER KOWALSK/ "/Zwss J Suez/A57" i INVENTO f v Arrmwsy Aug. 21, 1956 r w. KOWALSKI ETAL HIGH PRESSURE CONTACTS 2 Shee ts-Sheet 2 Filed Oct. 28, 1955 INVENTO W41. 7'52 Kan/445m Jam-a J 554630457 '25. Arm/aver HIGH PRESSURE CONTACTS Walter Kowalski, Milwaukee, Wis., and James J. Seaquist, lngleside, 111., assiguors to McGraw Electric Company, Milwaukee, Wis., a corporation of Delaware Application October 28, 1953, Serial No. 388,734

Claims. (Cl. 200-166) This invention relates to a high pressure stationary contact of the type adapted to receive a movable fuse or switch blade.

Electric switches classified as power switches have application in electrical circuits conducting current of high magnitude at comparatively high voltage. Therefore, it is imperative that joint resistance between the relatively movable parts of such switches be held to an absolute minimum so that accompanying power loss, manifested by heating of the switch, will be maintained at the lowest possible value.

Considerable diificulty has been experienced in power switches known heretofore in establishing the most preferable contact pressure between the stationary terminal and the movable blade received thereby during manufacture and in maintaining or restoring that pressure after extended use of the switch.

The switch terminal described hereinafter contemplates employment of an especially rugged pair of blade receiving fingers and auxiliary structure which facilitates establishment of a predetermined contact pressure exerted by the terminal and in maintaining that pressure throughout the life of the switch.

Accordingly, it is an object of this invention to provide a terminal which may be adjusted to exert a predetermined high contact pressure on a switch blade receivable thereby.

A further object of this invention is to provide apparatus for facilitating compensation for wear of the switch terminal at the scene of its installation.

Other objects will be expressly stated hereinafter or will be apparent to those skilled in the art.

Attainment of the aforementioned objects is described in the following specification and illustrated in the following drawings in which:

Fig. l is a front elevational view showing one embodiment of the invention.

Fig. 2 is a side elevational view of the embodiment shown in Fig. 1.

Fig. 3 is a fragmentary side view of the contact finger with the leaf spring assembly removed.

Fig. 4 is a front elevational view illustrating an alternative embodiment of the terminal with a variation in the contact pressure adjusting means.

Fig. 5 is an enlarged side view of the polysided contact pressure adjusting cam.

Fig. 6 is an end view of the cam shown in Fig. 5.

Fig. 7 illustrates the terminal shown in Fig. 1 at one stage of the assembly and pressure adjusting operation.

Fig. 8 is a side elevational view of a gage block used to establish the proper distance between the fingers of the terminal.

Like reference characters refer to like parts throughout the various views.

Fig. 1 illustrates the novel terminal comprising two upstanding laterally spaced fingers 1 and 2 preferably made of hard drawn copper and having a right angle bend to form base portions 3 and facing in opposed relation 2,760,034 Patented Aug. 21, 1956 at their ends 4. Hexagon head machine screws 5 secure the base portions 3 firmly to a mounting block 6 which has integral therewith a conductor adapter 7 for receiving a line conductor (not shown).

A tie-bar 29 is disposed through elongated holes 26 in each of the fingers. The shape of holes 26 can be most clearly comprehended by reference to Figs. 2 and 3. Tie-bar 29 also has a fiat spacer portion 27 integral therewith and interposed vertically between the fingers 1 and 2 for the purpose of limiting the minimum distance between the fingers which bear resiliently against the margins 28 of spacer 27. The spacer and tie-bar can, of course, be made in separate pieces provided the spacer is restrained in position between the fingers as suggested by the embodiment shown.

The end portions of tie-bar 29 are perforated by elongated holes 31 which normally receive a transverse stop pin 30. Pin 30 has its diameter reduced at its midsec-. tion to define a cylindrical restricted portion 30a having a length slightly exceeding the thickness of the tie-bar 29 as illustrated in Fig. 2.

A leaf spring assembly indicated generally by the reference numeral 12 is provided with congruent holes 11 which encompass the tie-bar 29. The assembly 12 is juxtaposed to the fingers 1 and 2 and is urged against them by reaction on the stop pin 30 through tie-bar 29.

The upper end 16 of the longest leaf 13 bears against a rectangular pad 17 silver soldered to the outer faces of fingers 1 and 2 preferably some distance above the margins 28 of spacer 27 Consequently, the force of the leaf spring assembly 12 urges the fingers 1 and 2 into contact relation with the margin 28 of spacer 27, the spacer thereby establishes the minimum distance between the fingers.

The lower end 18 of each leaf 13 is perforated by a hole 19 which embraces an anchoring pin 20 integral with and extending laterally from the mounting block 6. By insertion of thin perforated shims 25 over the anchoring pins 20 between the end 18 of leaves 13 and mounting block 6, increased loading of the leaf spring assembly 12 can be accomplished. It has been found that equal increments of increased pressure are developed on the fingers 1 and 2 for each additional shim 25 of the same thickness inserted under end 18 of leaf 13. Consequently, the pressure exerted by the fingers 1 and 2 on a switch blade (not shown) bridging between them can be readily established with the degree of accuracy required.

To further minimize the electrical resistance between a switch blade and the resilient fingers 1 and 2, silver inserts are provided in the fingers as indicated by the reference numeral 36. These inserts lie in the same vertical plane and are disposed oppositely of each other between fingers 1 and 2.

An alternative embodiment of the novel terminal is illustrated in Fig. 4- where its principal elements are shown substantially similar to the embodiment of Figs. 1, 2, and 3 heretofore described. The terminal shown in Fig. 4 has been modified by supplanting each anchoring pin 20 of Fig. l with a shoulder screw 40 threadedly engaged to the mounting block 6. Screws 40 have their diameter reduced at one end to define annular shoulders 41 and have their ends slotted as indicated by the reference char acter 42 for receiving a screw driver blade. The upper end 16 of leaf 13 bears against the pad 17 in a manner identical to that illustrated in Fig. l, but the hole 19 in the end 18 now has its circumferential margin bearing against the shoulder 41 of screw 40. It should be apparent that advancing and retracting of the screw 40 will effect corresponding decreasing and increasing load on spring assembly 12 and a like effect upon fingers 1 and 2.

As illustrated in Fig. 4, each of the leaf springs 13, 14, and 15 are stacked and perforated by a substantially congruent hole 11 for receiving the end of tie-bar 29 which passes horizontally therethrough. Tie-bar 29 is perforated at each end by an elongated hole 31 for receiving a polysided eccentric cam pin 45 which serves to retain the spring'assembly 12 against the pad 17 and the adjusting screw 40.

Cam pin 45 has its perimeter reduced intermediate its ends to define a cylindrical portion 48 having its axis displaced radially from the axis of the sides of the pin which define a polygon, shown greatly enlarged in Figs. and 6. \Vhen pin 45 is positioned as illustrated in Fig. 4, a flat face 46 thereof bears on the outer leaf spring 15. Longitudinal travel of pin 45 is prevented by reason of the shoulder portion 49 of cylinder 48 engaging the margins of elongated hole 31.

It will be readily apparent from Fig. 4 that rotation of the polysided cam 45, by engaging it with a Wrench, about the axis of cylindrical portion 48' will cause the sides 46 to sequentially advance and recede relative to the spring assembly 12, thereby causing corresponding changes in the loading of the spring assembly and consequent changes in the pressure which may be exerted by fingers 1 and 2 on a switch blade (not shown) bridging the space between them.

The terminal pressure adjustment obtainable by rotation of cam 45 used in conjunction with the adjustment obtainable by advancing and retracting screw 40 permits the preferable contact pressure exerted by fingers 1 and 2 to be developed within any practical range desired.

In assembling or maintaining the terminal heretofore described, it is desirable to ascertain in advance whether the terminal will seize a switch blade with which it will cooperate with adequate force. It would, of course, be slow and impractical to assemble and disassemble the terminal, alternately trying a switch blade therein, until it appeared that the proper pressure had been developed. Therefore, to facilitate assembly and maintenance of the terminal without resorting to cut and try methods, a testing means has been devised which permits convenient pre-establishment of the terminal pressure.

Attention is directed to Fig. 7 where the novel terminal pressure calibrating means are illustrated in relation to an embodiment of the terminal which is in a preliminary stage of assembly as compared to the completed embodiments of Figs. 1 and 2. It will be seen that fingers 1 and 2 are secured tightly to the mounting base 6 by screws 5. A leaf spring assembly 12 is then juxtaposed to the outsides of the fingers as shown in Fig. 7. Subsequently, a test-bar 60 is inserted horizontally through the hole 11 of the spring assembly 12 and through the fingers. The test-bar 60 is prevented from sliding completely through the springs and fingers by reason of a permanently affixed stop pin 63 with which test-bar 60 is provided. A gage block 65, having a Width equal to that of a switch blade (not shown), is inserted between the fingers 1 and 2 and allowed to rest on test-bar 60. A channel 66 in gage 65 engages the test-bar 60 and prevents its inadvertent lateral removal.

It will be observed that test-bar 60 has an elongated hole 62 through its face. Part of hole 62 is included within the spring assembly 12 but, another portion thereof is exposed adjacent to outer leaf spring 15.

While the leaf spring assembly 12 is compacted snugly, as a result of an endwise force being manually exerted on the test-bar by the assembler, a straight shanked removable pin 61 is inserted in the exposed portion of hole 62. Pin 61 then has its axis parallel to the plane of the outer leaf 15 and its outer periphery may bear firmly thereagainst.

If the pin 61 fits loosely under the circumstances described in the last paragraph, it is an indication that additional shims 25 must be placed over anchoring pin to shift the spring assembly 12 farther away from the fingers 1 and 2 at its lower end. This may be accomplished in a moment by removing pin 61 and sliding the test-bar 60 from the terminal to allow removal of the spring assembly 12 to permit placement of a shim 25 over anchoring pin 20.

The spring assembly 12 is then replaced as shown in Fig. 7 and the bar 60 again inserted therethrough. Generally, after only one try, the correct shimming 25 will be inserted, as will be readily apparent to one calibrating the terminal, by reason of the pin 61 fitting hand tight as it passes through hole 62 adjacent leaf 15. When this snug, hand tight condition prevails, final assembly can be completed by removing the test-bar 60 and gage block 65 from the terminal and substituting therefor the tie-bar 29 shown in Fig. 1 and securing it against sliding outward by inserting a pin 30 at each end.

It is to be appreciated that during the calibrating operation described in detail heretofore, the spring assemblies 12 are not fully loaded when the straight pin 61 is disposed in the test-bar 60 nor does the gage block 65 necessarily have to be of the exact width of the removable switch blade (not shown). The important feature of the calibrating operation inheres in a definite relationship being established between conditions during the adjustment of the terminal and after final assembly. Hence, during final assembly it will be found necessary to coerce the spring assemblies 12 together by spanning the spring assemblies 12 with a C-clarnp and compressing it to obtain clearance for insertion of pin 30. After insertion of pin 39' and removal of the C-clamp, the spring assemblies will remain somewhat pre-loaded and it follows that fingers 1 and 2 may be flexed slightly inwardly toward each other.

From the foregoing specification, it is apparent that a novel spring loaded stationary terminal has been described together with novel means for calibrating it. Thus, the desired contact pressure exerted by the terminal can be predetermined and held uniform during manufacture or throughout the life of the switch. Moreover, it will be obvious to those skilled in the art that the test-bar and gage block combination may readily be adapted for use with terminals having slightly different proportions by merely shortening or lengthening hole 62 and changing the dimensions of gage block 65 accordingly.

It is claimed:

1. In an electrical terminal, a pair of spaced resilient fingers for engaging a movable member therebetween, mounting means supporting said fingers in spaced relationship, spring adjustable anchoring means projecting laterally from said mounting means, oppositely disposed laminar leaf spring assemblies biasing said fingers toward each other, ends on said leaf springs, one of said ends adjacent said fingers and the other of said ends embracing said anchoring means, opposed contact inserts disposed interiorly of said fingers in substantially the same plane as said one of said spring ends, a tie-bar extending through said fingers and springs and including an integral spacer portion between and in bearing relation with said fingers, and a manually rotatable polysided pin having a side in bearing relation to said spring assemblies, respectively, intermediate their ends, said polysided pin having a cylindrical central portion with its axis eccentric to the axis of the polygon defined by said polysided pin, said central portion being engaged by said tie-bar, said pins urging said spring assemblies against said fingers in opposition to the reaction thereagainst effected by said spacer.

2. A method for adjusting an electrical switch terminal comprising fixedly mounting two spaced upstanding perforated fingers on a base, juxtaposing perforated leaf spring assemblies against said base and fingers projecting through said fingers and springs a test-bar having at one end a fixed spring engaging pin and at the other end an elongated hole until stopped by said fixed pin, inserting a gage block between said fingers, manually urging said fingers and springs against said gage block, inserting a straight pin in said elongated hole in the test-bar adjacent a leaf spring assembly, shimming said leaf spring under one end until it is in firm contact relation to said straight pin, removing the test-bar and gage block, substituting a tie-bar therefor, and inserting pins through said tie-bar to permanently position the tie-bar.

3. A method for adjusting an electrical switch terminal comprising fixedly mounting two spaced upstanding perforated fingers on a base, juxtaposing perforated leaf spring assemblies against said base and said fingers, projecting through said fingers and springs a test-bar, said test-bar having a spring engaging end and a detachable end, said ends being in predetermined spaced relation to each other, inserting a gage block between said fingers, manually urging said fingers and springs against said gage block, attaching said detachable end to said test-bar, adjusting the pressure exerted by said leaf springs until in firm contact relation to said test-bar ends, removing the test-bar and gage block, substituting a tie-bar therefor, and affixing said tie-bar into position relative to said terminal.

4. An electrical terminal comprising a pair of spaced resilient fingers for engaging a movable member therebetween, mounting means supporting said fingers in spaced relationship, spring anchoring means projecting laterally from said mounting means, a leaf spring juxtaposed to each finger, respectively, said spring having one end in compressive relation against said finger and another perforated end engaging said spring anchoring means, a tiebar extending'laterally through said fingers and spring and including an integral spacer portion between and in bearing relation with said fingers, spring retaining means fastened to said tie-bar adjacent said spring for urging said spring against said fingers in opposition to the reaction thereagainst effected by said spacer.

5. An electrical terminal comprising a pair of spaced resilient fingers for engaging a movable member therebetween, mounting means supporting said fingers in spaced relationship, spring anchoring means projecting laterally from said mounting means, laminar leaf spring assemblies juxtaposed to each finger, respectively, each assembly including leaves of different lengths, the longest of said leaves having one end in compressive relation against a finger and another perforated end engaging said spring anchoring means, opposed contact inserts disposed interiorly of said fingers in substantially the same plane as said one end of said longest leaves, a tie-bar extending laterally through said fingers and said spring assemblies and including an integral spacer portion between and in bearing relation with said fingers, spring retaining means fastened to said tie-bar adjacent each spring assembly for urging said spring assemblies against said fingers in opposition to the reaction thereagainst efiected by said spacer.

References Cited in the file of this patent UNITED STATES PATENTS 1,978,246 Bauerschmidt Oct. 23, 1934 2,221,607 Samzelius Nov. 12, 1940 2.433.115 Green Dec. 23, 1947 

